The S4's 4.2-liter V8 is more compact and lighter than Audi's previous 4.2 and weighs about the same (430 lb) as the biturbo V6 in the current S4. To fit the engine in the narrow engine bay, the chain drive for the camshafts and ancillaries was moved to the output end of the V8, reducing its length by 55mm. Weight was shaved from each piston (by 70 grams) and connecting rod (by 66 grams), improving power to weight ratio from 12.8 lb/hp to 10.5 lb/hp. The refined internals and five-valve-per-pot cylinder head combine to produce an exceptionally elastic powerband, the tach needle ever eager to reach for the 7200-rpm electronic cut-off. Peak output of 339 bhp occurs just 200 rpm shy of redline. Maximum torque is 302 lb-ft at only 3500 rpm and continues unchecked through 4500 rpm. However, a hefty 221 lb-ft is already underfoot by 1100 rpm, Even with such impressive performance-related numbers, the 4.2 meets the EU IV emissions limits.